There have conventionally been known a high-pressure mercury lamp, an excimer discharge lamp, and the like as a light source device using gas discharge. There has also been known a gas discharge device using an ultraviolet light-emitting phosphor as an ultraviolet light source (for example, see Patent Document 1). Also, an external electrode type gas discharge device having a thin tube configuration suitable for a configuration of a flat light source has been known (for example, see Patent Documents 2, 3, and 4).